Medical devices are highly regulated by multiple regulatory bodies and compliances. On the other hand, end users expect exceptional performance, effectiveness, and safety from the device they are using. This compels medical device manufacturers to define and implement medical device testing strategy that turns to be effective throughout the development cycle — starting from the concept and design phase to production stage.
A medical device testing strategy must incorporate compliance processes and technical testing strategies for better performance and effectiveness of medical devices. Manufacturers need to have a strong testing strategy in place right from the design stage, as performing an exhaustive testing of a produced device is ineffective and inefficient.
For e.g. A medical device manufacturer needs to test each functionality of the medical device right from the design stage for a better test coverage. If they test manufactured devices for the functionalities and find issues with the device, it will be very costly and time consuming to go back to the design phase and find appropriate solutions for the issues.
Devising an effective medical device testing strategy
Testing team should utilize design team as a source of knowledge. Design input can help to derive the test structure that matches with the hardware, software or other technical requirements. The design classmodes, effects, and criticality analysis (FMECA) can be used to derive test requirements of the device for risk mitigation.
An effective medical device testing strategy needs several sets of test requirements.
These test requirements are based on the component specification, manufacturing process, and other critical functional specifications of the device. Test requirements define and describe setup conditions, actions, and expected response constraints for each experiment defined in the test steps.
These sets of requirements are required to smoothen test implementation as tests are carried out continuously at different stages of the complete manufacturing process, from component selection to a final assembly of a medical device, and each stage has different requirements and different parameters to be satisfied.
Applying medical device testing strategy
The highest level of medical device test strategy takes the production testing of components, sub-assemblies, and the finished product into account for technical testing. Specific hardware and software requirements for each test stages are considered with the measurement methods and expected output in the test strategy.
An effective test strategy is a product level activity that brings a complete test set into account for each stage of the product development. It considers defects in a test model at each stage and correlates defects to optimize the overall performance of the device. The desired output for each stage is defined by the strategy to ensure overall effectiveness.
In the validation process, the system is divided into small blocks without losing the traceability to the original test strategy and then the testing starts with specified requirements for each block in the system. Validation methods for each block are customized based on risk-based analysis for better fitting of the test strategy. The high-level test strategy provides a strong reference for technical reviews of the device and its validation.
In order to perform testing to the highest standards, medical devices must undergo solid electronic testing. Most of class II and III medical devices have microprocessor at its core. Hence, medical device testing starts with a microprocessor testing.
For an effective testing of transistors inside a microprocessor, it must provide access to their interconnections. However, the catch is, the testing team should carry out microprocessor chips’ testing before installing it into a printed circuit board (PCB) for an increased testing effectiveness.
Tests for integrated circuits consider their logic gate functions and interconnection between them. Well-suited test methods can be selected from several industry-used test methods based on the requirements.
After attaching all the components to the PCB, testing of mounting and interconnection process is the next priority. In this phase, the testing team should use common defect of an assembly model where they try to identify the wrong component, missing component, open interconnect, shorted interconnect, etc., in the PCB assembly process.
Modern test equipment delivers the physical access to the PCB and allows the direct measurements of components in small groups. It is important to ensure that these small groups of components in the PCB do not affect the functioning of the system as a whole. Hence, functional testing is crucial for all the functions, which can be influenced by parameters of other components. Similar PCBs are allowed for functional testing, but it is insufficient for finding common manufacturing defects. Hence, additional troubleshooting may be required to identify specific repairs.
Automating the test
A test automation system is an electronic system developed with the purpose and consists of a computer, instruments and a software to carry and control test process. There are certain commercial test automation systems available in the market in accordance with industry standards. However, the testing team can use a customized test system based on the need and requirements.
While using test automation system, the testing team may need to change the strategy based on the available test options for each stage of medical device development. It may restrict the testing team with constraints by limiting the implementation methods.
In case of testing complex medical devices with extremes of voltage and current requirements, the testing team may face challenges in the test automation environment due to the limited ability to generate test cases and measuring the accuracy of the test. Ideally, automated test implementation is a matter of simultaneous hardware and software design. The test set for a certain stage in the manufacturing process flow is defined in the test strategy by the test specifications allocated for that particular stage. We need to break down those test specifications into software and hardware requirement specifications according to the test system software and interface hardware, respectively.
Normally, system specifications are derived from medical device design stage, but there are certain specifications that we need to derive from the production test environment like compliance with security and data integrity. Mechanical design, coding and electrical design of test system result from all those specifications. For an established facility, where several medical devices have been designed, manufactured and tested, common blocks of hardware and software are re-used to simplify the process.
Once everything is in place, the medical device test system must be validated, including software and hardware. The process of software and hardware validation for medical devices must be detail specific. The purpose of validation is to test if the device meets specific user needs or not. Hence, the structure and approach are very crucial to apply validation methodology.
Validation must be carried on an initial production unit. In other words, a device for validation has to be built into the production environment. The process requires involving the end-user and it should be tested either under simulated use or under the actual use. Validation tests are required to validate that the medical device functions as expected and meets the users’ needs.
The initial approach for validation should start with unit testing of a set of stages in the process and then a complete system could be validated as a whole. Considering the complexity of the system, it is an overwhelming task for most of the automation systems. In that case, a divide and conquer validation approach is a better choice.
Integration testing involving complete system is a necessary practice, which should be a culmination of a coordinated validation protocol and not the entire plan.
A functional testing of a medical device consists of testing different functional blocks such as operating system, instruments, hardware etc., which must be validated for their intended use. The process starts with manufacturer’s specifications or a subset of specifications that can be applied to each block from design and test team.
The testing team should work with the manufacturing team to validate those specifications and then testing and verification of the performance of individual block should be done to document the result, which should be then reviewed. The functional block test comes handy for validation of custom developed hardware or software for medical devices.
Verification is a process to confirm whether the examination and provision of objective evidence that specified requirements of the device have been fulfilled. Verification process starts with clear and well-defined product requirements. These product requirements must be measurable in order to verify. We must know what the answer should be as verification is not an experiment.
The process follows several formal protocols. It suggests comparing current product requirements with the requirement of an already approved product. The verification process must contain full methodology or a reference to standard methodology, statistical justification for sample size, statistical plan for data analysis and more. It also needs to specify details on acceptance criteria and procedure to follow in case of the failed verification.
If a verification is failed, it must go through a further investigation to determine the requirement, which could not be verified and whether that requirement is valid or achievable in the current design or not. Further investigation may provide information whether the product requirement can be updated and re-verified.
A strongly defined and implemented medical device testing strategy can save dollars for manufacturers and ensure that devices meet the end user expectations. It also decreases the risk of devices recall. From the business standpoint, it is advisable to collaborate with organizations having domain expertise in testing as it decreases the overall risk and time required for testing.
eInfochips has been an innovation partner for many medical device companies, including Fortune 500 firms. We have experience throughout medical devices lifecycle stages, namely product ideation to design & development, component engineering, product re-engineering, testing and verification & validation, sustenance engineering, and regulatory compliances.
For more details, download the success story of a California based medical device company for which we developed a portable, battery-operated insulin pump with a software controlling dosage.